Electrical apparatus bushing



Dec.

L. J. LINDE ETAL ELECTRICAL APPARATUS BUSHING Filed Spt. 14, 1944[fivenbors Leonard J. Linde Nicholas P. Aroma,-

BenJ amin E. Spiro Their Abtovne Patented Dec. 21, 1948 ELECTRICALAPPARATUS BUS KING Leonard J. Linde, Drexel Hill, Nicholas F. Arone,

Upper Darby, and Benjamin E. Spiro, Philadelphia, Pa., assignors toGeneral Electric Com- Y pany, a corporation of New York ApplicationSeptember 14, 1944, Serial No. 554,100

' 5 Claims. (Cl. 174-152) Our invention relates to electrical apparatus,such as circuit breakers or the like, wherein an insulated electricalconductor generally referred to as a bushing extends through a wall orcover of an electrical housing or the like. Specifically our inventionis concerned with a new and improved electric bushing for electriccircuit breakers or the like. I

Bushings for electric circuit breakers, of the type particularly adaptedfor use with metal-clad switchgear, have been constructed by placing aconductor within a treated paper or fabric insulated tube. Thisinsulated tube then was machined along a part of its length from one endthereof to produce a body portion of reduced cross section after which afianged metal supporting cylinder was pressed over this reduced bodyportion. Finally an insulating sleeve for backing up the supportingcylinder was pressed over the remaining portion of reduced crosssection. This cult breaker which happens to be particularly adapted foruse in metal-clad switchgear. This circuit breaker is in many respectssimilar to the circuit breaker disclosed and claimed in Linde Patent2,293,513, granted August 18, 1942, and assigned to the same assignee asthe present applicatl0n.. such a breaker comprises a plurality ofconductor studs or bushings such as I and 2, each'provided witha'suitable mounting flange so that the conductor stud or bushing may besupported where it passes through the wall or housing 3 of the circuitbreaker, generally indicated construction required the close fittingtogether of the long machined surfaces of the several componentcylindrical members, otherwise breakdown often resulted when highvoltage impulses were applied.

Our inventionis particularly concerned with providing a new and improvedbushing for electric circuit breakers or the like and which, because thesupport therefor is fabricated, is simpler and less dependent upon theclose fits of its component parts, and which arrangement results in amore satisfactory bushing.

It therefore is an object of our invention-to provide an improvedapparatus of this character, which apparatus shall be simple inconstruction, effective in use and inexpensive to manufacture.

Further objects and advantages of our invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize our invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of our invention reference may be had tothe-accompanying drawing in which Fig. 1 'isan elevationalview partly insection of an electric circuit breaker employing bushings embodying ourinvention; Figs. 2a, 2b, 2c, 2d and 2e illustrate successive steps inmanufacturing the bushing embodying our invention; Fig. 3 is a sectionalview taken on line i=4 of Fig. 2e, and Fig. 4 is a view similar to Fig.2e illustrating a modified bushing made in accordance with ourinvention. 7

Referring now to Fig. 1, we have illustrated our invention as applied toa well known form of cirat 4. The bushing I in the case of a breakersuch as is disclosed in the Linde patent, is somewhat shorter than thebushing 2. We have illustrated the complete bushing i in Fig. 2e and thecomplete bushing 2 inFig. 4.

The bushing I includes. an axial conducting stud or core member 6 formedof copper or the like,

having a spherical plug type terminal 8 formed at one end thereof forengaging self-aligningiy with a cooperating resilient socket typeterminal. The end of conductor 5 opposite from terminal 6 is providedwith a suitable configuration I, so as to be adapted for connection to acontact such as the stationary contact of the circuit breaker 4. Exceptfor the terminal 8 and the rectangularly configured portion 1, conductor5 preferably comprises a cylindrical rod,

In order to insulate conductor 5 from the grounded portions of thecircuit breaker 4 including the housing 3, the conductor 5 is firstpressed into a cylinder or tube 8 of insulating material, the tube 8being slipped over the end 6 of conductor 5 after an end thrust washer Ihas been placed upon the rod 5 for abutting the end portion 1as'indicated in Fig. 2a. Preferably this cylinder is constructed oflaminated sheet organic material united by an adhesive binder. A portionof the cylinder 8 intermediate the ends thereof is undercut bymachiningso as to form a portion of reduced circular cross section 9. This stepis preferably performed after the cylinder 8 is pressed around conductor5. Fig. 2a illustrates the bushing after the machining operation oncylinder 8 is performed.

In Fig. 2b there is shown a perspective view of a pair of fiangedsemi-cylindrical metal members Ill and II which are constructed so as tofit around the portion of reduced cross section 9 and completely envelopthe same. The flanges I2 associated with the members It and II providethe means for supporting the conductor stud at the point where it passesthrough the wall or housing 3 of circuit breaker 4. The ends of thesemi-cylindrical members I and ii.

semi-cylindrical members ill and Ii preferably are tapered as indicatedat It so that when they are applied to the insulating cylinder 8 theyunderlie the surface of the cylinder 8, thereby raising the corona pointin this region of high electrlcal'stress to a safe value therebypermitting the improved bushing constructed according to our inventionto withstand the desired impulse voltages.

The next step'in the process of constructing the bushing or conductorstud of our invention comprises cementing the semi-cylindrical flangedmetal members i and II to the portion of reduced cross section 9 ofcylinder 8. We have found that a phenolic modified polyvinyl butyralresin cement is very satisfactory for this purpose. This cement isapplied to the holding surfaces and the semi-cylindrical members ill andII then are clamped with pressure about the cylinder 8 and baked forapproximately an hour at 250 C. in order to set the cement. The bushingor conductor stud with the flanged semi-cylindrical members cementedthereto is afterwards placed in a lathe to true up the cylindricalsurfaces of the flanged members ll and if as well as to insure that themounting surfaces of the flanges I! are perpendicular to the axis of thebushing. At the same time, an annular groove i4 is machined into thesemi-cylindrical members, as is clearly indicated in Fig. 2c. Theconductor stud or bushing disclosed in Fig. 2c illustrates theappearance thereof after the above steps in the process of manufacturehave been performed.

In Fig. 2d there is illustrated a perspective view of a thin-walledmetal tube i5, preferably formed of brass or the like, having an insidediameter such that it is readily slidable over the cylinder I and thetrued curved surfaces of the cemented halves Ill and ii. A small hole I6is provided in one of the semi-cylindrical flanged members, as isclearly indicated in Fig. 3. The thin-walled metal cylinder i5 now is,slid over the terminal end 6 of the conductor 5 to surround thesemi-cylindrical members I 0 and il above the flanges i2. To preventthis tube i5 from rotating, a portion of the tube indicated at H inFigs. 2c and 3 is indented into the hole I 8 in the semi-cylindricalmember i ll. Thereafter the cylindrical tube or sleeve i5 is deformed byspinning it, as indicated at it, into the annular groove l4 therebyproducing a tightly gripping retaining ring which reinforces thecemented The now completed bushing, as indicated in Fig. 2c, is readyfor installation in the circuit breaker I and for which purpose suitablemountin bolts are used which extend through the openings I9 in flangesi2 and through corresponding holes in the breaker housing 3.

In Fig. 4 we have illustrated the conductor stud or bushing 2 which isconstructed in a manner very similar to the bushing i described above,except that the undercut portion of the insulating tube is somewhatlonger and consequently the semi-cylindrical members are correspondinglylonger. The conductor stud or bushing 2 also comprises a conducting rodhaving a spherical plug type terminal at one end thereof and a suitablerectangularly configured portion 2| at the other end, which may beadapted so as to support the pivoted contact of the above-mentioned typeelectric circuit breaker. A thrust washer 22 is slipped over theterminal end 20 of the conducting member until it engages the portion1|, after which the insulating tube 23 is slipped over the terminal 20and pressed into position. .As in bushing I, the portion of reducedcross section 24 intermediate the ends of the insulating tube 23preferably is machined after the tube is assembled on the conductingmember. The flanged semi-cylindrical members such as 25, only one ofwhich is shown in Fig. 4 since the other is hidden from view, are thencemented to the portion of reduced cross section 24 after which thesesembcylindrical members are trued up in a lathe and the flanges 28associated with the semi-cylindrical members 25 are machined on theirmounting face so as to be truly perpendicular with the axis of thebushing. Also two annular grooves similar to the annular groove ll ofFig. 2c are cut in the semi-cylindrical members, one above and one belowthe flanges 28. A clamping sleeve 21 substantially identical withclamping sleeve i5 is slipped over the terminal end II of the bushing 2and held from rotatin by an indentation 28 while the sleeve is deformed,as by spinning into the annular groove indicated at 29. Similarly asleeve 30 is slipped over the other end of bushing 2 so as to clamp thelower ends of the semi-cylindrical members such as 25. The clampingsleeve 30 is also prevented from rotating by indenting a portion thereofas indicated at 3i into an opening formed in one of the semi-cylindricalmembers 25 after which the clamping sleeve 30 is deformed by spinning itinto the associated annular groove, as indicated at 32.

It will be obvious that the above-described cementing method used in themanufacturing process of the bushing 01' our invention produces anexceedingly strong adhesive Joint between the cylinder of insulatinmaterial and each curved portion of the flanged supporting members inorder for these Joints to withstand the strain from the subsequentintermediate machining, grooving and spinning operations as alreadydescribed. Actually, we have found these cemented Joints to be adequatefor supporting the bushing through the agency of its composite flangedcylindrical supporting structure without benefit of any furtherreinforcement; so that the spun sleeves i5, 27 and 32 may be regardedrather as providin additional security for the flanged halves and alsofor imparting an appearance of solidarity to the finished product.

It will be appreciated from the above explanation that we have providednew and improved electric bushings which are simple to manufacture inthat they eliminate the requirement of close flts which are difllcult tomaintain and which necessitates accurate and long machined surfaces. Inaddition the tapered portions ll of the semi-cylindrical members in andIi are effective in raising the corona point to a safe value whereby thebushings 0r conductor studs 01 our invention withstand higher impulsevoltages than in comparable bushings as constructed heretofore.

Although we have disclosed particular embodiments of our invention, itwill be obvious to those skilled in the art that modifications may bemade without departing from our invention and we intend in the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. A terminal bushing for an electric switch comprising a conductingmember including a terminal formed thereon, an insulating sleeve havinga reduced mediate the ends thereof enclosing a substantial "portion ofsaid segmental members so as tightl said portion oil reduced crosssection, and a thin walled metal tube surrounding said semi'-cylin-'drical members so as tightly to grip said members to reinforce the same.a

2. A bushing for an electric switch comprisin a conducting member, aninsulating sleeve enclosing a substantial portion of said conductingmember, supporting means encircling said sleeve including a pair offlanged semi-cylindrical members cemented to said sleeve, and a thinwalled metal tube surrounding said semi-cylindrical members so astightly to grip said members to reinforce the same.

3. A bushing for an electric switch comprising aconducting member, aninsulating sleeve having a reduced cross section portion intermediatethe ends thereof enclosing a substantial portion of said conductingmember, supporting means encircling said sleeve including a pair offlanged semi-cylindrical members cemented to said portion of reducedcross section. a thinwalled metal tube surrounding said semi-cylindricalmembers, and means for causing said tube tightly to grip and reinforcesaid semi-cylindrical members comprising an annular groove in saidsemicylindrlcal members and a cooperating deformed portion on said metaltube.

4.-A bushing for electric apparatus comprising a central rod-likeconducting core, an insulating cylindrical sleeve completely surroundingpart of the length .of said core, supporting means comprising aplurality of segmental component members arrayed circumferentiallyaround a portion of said sleeve, each said'member including a curvedportion conforming to the curvature of said sleeve, cementing materialinterposed between said segmental members and said sleeve to form a bondtherebetween, and a thin walled metal tube surrounding the curved togrip said members to provide reinforcement for the bond between saidsegmental members and said sleeve.

5. A bushing for electric apparatus comprising a central rod-likeconducting core, an insulating i cylindrical sleeve completelysurrounding part of the length of said core, an annular recess aroundsaid sleeve, supporting means comprising a plurality of segmentalcomponent members arrayed circumferentially around said annular recess,each said member including a curved portion conforming to the curvatureof said annular recess, cementing material interposed between saidsegmental members and said sleeve to form a bond therebetween and an in-V dented metal tube surrounding the curved por-.

tion of said segmental members so as tightly to grip said members toprovide reinforcement for the bond between said segmental members andsaid sleeve.

LEONARD J. Iii-Non;

NICHOLAS r. ARONE.

BENJAMIN n BPIRO.

REEERENoEs crrEn The following references are of record in the file ofthis patent:

